A new glutamate dehydrogenase from Halobacterium halobium with different coenzyme specificity |
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| Institution: | 1. Department of Medical Microbiology and Immunology, University of Toledo College of Medicine and Life Sciences, Toledo, OH 43614, USA;2. Lumigen Instrumentation Center, Department of Chemistry, Wayne State University, Detroit, MI 49202, USA;1. Gas Processing Centre, College of Engineering, Qatar University, P. O. Box 2713, Doha, Qatar;2. Department of Chemical Engineering, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar;3. Mining Studies & Research Centre, Faculty of Engineering, Cairo University, Egypt |
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| Abstract: | - 1.1. Halobacterium halobium has two chromatographically distinct forms of glutamate dehydrogenase which differ in their thermolability and other properties. One glutamate dehydrogenase utilizes NAD, the other NADP as a coenzyme.
- 2.2. The NADP-specific glutamate dehydrogenase (EC 1.4.1.4) was purified 65-fold from crude extracts of H. halobium.
- 3.3. The Michaelis constants for 2-oxoglutarate (13.3 mM), ammonium (3.1 mM) and NADPH (0.077 mM) indicate that the enzyme catalyzes in vivo the formation of glutamate from ammonium and 2-oxoglutarate.
- 4.4. The amination of 2-oxoglutarate by NADP-specific glutamate dehydrogenase is optimal at the pH value of 8.0–8.5. The optimal NaCl or KCl concentration for the reaction is 1.6 M.
- 5.5. None of the several metabolites tested for a possible role in the regulation of glutamate dehydrogenase activity appeared to exert an appreciable influence on the enzyme.
- 6.6. NAD- and NADP-dependent glutamate dehydrogenases from H. halobium showed apparent molecular weights of 148,000 and 215,000 respectively.
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